Commentary On Section 15.5

The reason for the required 50% load is that it is used as a 'preload' which settles the sheeting to a stable position before proceeding with the test.

It is suggested that the increments be at 10% intervals.

Although deflection under load is not regarded as a design criterion, it is an important indicator of stress leading to permanent strain.

Residual deflection, after all load has been removed is regarded as the only deflection criterion that will affect the performance of the sheeting.